John J. Rambo was born on July 6, 1946 in Bowie, Arizona to a Native American (Navajo) father (R. Rambo according to the last film) and an Italian American mother (Marie Dragoo). However, in Rambo: First Blood Part II, Marshall Murdock states that Rambo is of Native American Indian/German descent. Rambo graduated from Rangeford High School, and then was drafted into the United States Army at the age of 17 on June 8, 1964. He was deployed to South Vietnam in September 1966. He returned to the U.S. in 1967 and began training in the Special Forces (Green Berets) at Fort Bragg, North Carolina. In late 1969, Rambo was re-deployed to Vietnam. In November 1971, he was captured by North Vietnam forces near the Chinese-Vietnamese border and held at a POW camp, where he and other American POWs were repeatedly torture. Rambo escaped captivity in May 1972, but was then re-deployed. At some point in his military career he also apparently received training in flying helicopters.

Upon his return to the U.S., Rambo discovered that many American civilians hated the returning soldiers, and just like the other returning soldiers, he himself was subject to humiliation and embarrassment by having anti-war "hippie" throw garbage at him, call him "baby killer", and exclude him from society. His experiences in Vietnam and back home resulted in an extreme case of post-traumatic stress disorder of a sort that does not seem to have ever manifested in reality. At the same time, inner questions of self identity and reflectiveness cause Rambo to lash out at society rather than handling difficult situations in a "civilized" manner. This is where First Blood picks up from.

The original novel is similar to its film adaptation, but contains several notable differences.